The invention relates to rock crushers as used in mines or in aggregate producing industries.
Prior art rock crushers can be classified into two main types, namely impact crushers and compression crushers. Impact crushers include hammer crushers, rotor impactors, vertical centrifugal impact crushers and cage mill crushers. Compression crushers include jaw crushers, gyratory crushers, cone crushers, roll crushers and pan crushers. Each type of crusher has one or more advantages for particular applications, and correspondingly, each type of crusher also has disadvantages which make them inappropriate for certain applications. The selection of a particular type of crusher is usually dependent on the material to be crushed and the final application of the crushed material, as well as cost and maintenance considerations.
Impact crushers have rotating impact parts which wear rapidly, are not very successful in crushing very hard minerals or ordinary rocks, and cannot easily handle large sized material over 1 meter. Also, considerable power is consumed in the impacting process, and vibration is severe.
Some compression crushers have similar problems to impact crushers, for example roll crushers are prone to rapid wear, and once a portion of a roll is worn, rate of wear of that portion increases as material to be crushed tends to be concentrated on the worn portion of the roll. Also, roll crushers cannot handle large sized material, and are usually limited to material less than 0.2 meters. While jaw crushers can handle material larger than 1 meter, they have a relatively low efficiency with respect to time as they cannot be operated at high speed due to severe vibration of moving jaw parts which tend to follow complicated movements. The complicated movements of the jaw parts causes severe balancing problems, and because complete balancing is essentially impossible, the machines are operated at a relatively low speed to avoid excessive vibration. In addition, operation of a jaw crusher can be divided into two periods, namely a compression period and a releasing period. During the compression period, most of the material between the jaws is crushed at the same time, and this requires relatively high forces which are generated for a relatively short period of time by an eccentric shaft and bearings. During the releasing period, no effective work is being performed, and this reduces overall operating productivity with respect to time.
Cone crushers have a relatively high efficiency with respect to time when crushing small size material, which is preferably less than 0.15 meter but with special design the cone crusher can handle material up to 0.4 meters. Gyratory crushers have similar characteristics to cone crushers, but in general can handle larger material than the cone to crusher, i.e. material up to 1.5 meters. However, a gyratory crusher that can handle the same large size material as a jaw crusher is very much larger than the jaw crusher, and is correspondingly far more costly. A major advantage of both the cone crusher and the gyratory crusher is that material is crushed continuously between a rotor and stator, and thus application of forces on bearings and other portions is essentially continuous and relatively moderate. Thus, cone crushers and gyratory crushers can operate more efficiently with respect to time by applying essentially continuous and relatively moderate forces to the material than when compared with the relatively high forces, applied for short time intervals, that occurs with jaw crushers. However, cone crushers and gyratory crushers are more complicated and costly than jaw crushers, and usually cannot handle the relatively large material handled by jaw crushers.
In all rock crushers known to the inventor, many factors must be considered when selecting a crusher for a particular application. For example, the ratio of average size of raw material at the inlet, to average size of finished product at the outlet is referred to as "reduction ratio", and if only one machine is to used on a site, the reduction ratio for that one machine is generally larger than the reduction ratio of individual machines if several machines are to be used in series with each other on a site. Also, a limiting factor in most crushing operations is determined by maximum size of primary material that is fed into the primary crusher at the site and maximum "sliding angle" of the inlet as will be described with reference to FIG. 19.